Gaist astrology guide
House systems: why houses can differ between charts
Planetary zodiac positions remain the same, but house systems divide the space between the chart angles in different ways. A planet may therefore appear in a different house when the system changes.
What is calculated?
Birth time and location determine the local orientation of the sky, including the ascendant, Midheaven and house cusps. Astrology associates the twelve houses with areas of life, making an accurate time especially important for house placement.
Placidus
Placidus is common in modern Western astrology. It is an unequal, time-based system, so houses can vary in size. Calculations can become problematic at high geographic latitudes. Gaist uses Placidus by default when no other system was selected or when a legacy saved chart has no system recorded.
Whole Sign and equal houses
Whole Sign makes the complete rising sign the first house and each following sign another house. Equal houses instead begin at the exact ascendant and place subsequent cusps every 30 degrees. Both use equal-sized houses, but their boundaries differ.
Koch, Porphyry and other systems
Koch is another unequal, time-based system. Porphyry divides each region between the principal angles into three equal sections. Regiomontanus, Campanus, Alcabitius and topocentric houses use their own geometric or temporal constructions, producing different cusps.
What happens in polar regions?
Some time-based systems cannot be determined reliably for every moment near the polar circles. If a selected method yields no valid result there, Gaist may fall back to Porphyry for that calculation. The system actually used is shown with the result and saved charts.
Which system should I choose?
Astrology has no universally binding winner. Consistency matters most when comparing charts. Beginners can stay with the default Placidus system and later compare deliberately, focusing on changes caused by shifted house cusps.
What does not change?
Changing the house system does not alter the birth data, astronomical planetary positions or aspects between planets. It mainly changes house cusps and the assignment of planets to areas of life. The ascendant and Midheaven remain astronomical angles, although systems integrate them differently.
Astrological interpretations are intended for entertainment, inspiration and self-reflection.